The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that miss exiting the narrow pupil. In humans the pupil is round, but other species, such as some cats, have vertical slit pupils, goats have horizontally oriented pupils, some catfish have annular types. In optical terms, the anatomical pupil is the eye's aperture and the iris is the aperture stop; the image of the pupil as seen from outside the eye is the entrance pupil, which does not correspond to the location and size of the physical pupil because it is magnified by the cornea. On the inner edge lies a prominent structure, the collarette, marking the junction of the embryonic pupillary membrane covering the embryonic pupil; the pupil is a hole located in the centre of the iris of the eye that allows light to strike the retina.
It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that miss exiting the narrow pupil. The iris is a contractile structure, consisting of smooth muscle, surrounding the pupil. Light enters the eye through the pupil, the iris regulates the amount of light by controlling the size of the pupil; this is known as the pupillary light reflex. The iris contains two groups of smooth muscles; when the sphincter pupillae contract, the iris constricts the size of the pupil. The dilator pupillae, innervated by sympathetic nerves from the superior cervical ganglion, cause the pupil to dilate when they contract; these muscles are sometimes referred to as intrinsic eye muscles. The sensory pathway is linked with its counterpart in the other eye by a partial crossover of each eye's fibers; this causes the effect in one eye to carry over to the other. The pupil gets narrower in light; when narrow, the diameter is 2 to 4 millimeters.
In the dark it will be the same at first, but will approach the maximum distance for a wide pupil 3 to 8 mm. In any human age group there is however considerable variation in maximal pupil size. For example, at the peak age of 15, the dark-adapted pupil can vary from 4 mm to 9 mm with different individuals. After 25 years of age the average pupil size decreases, though not at a steady rate. At this stage the pupils do not remain still, therefore may lead to oscillation, which may intensify and become known as hippus; the constriction of the pupil and near vision are tied. In bright light, the pupils constrict to prevent aberrations of light rays and thus attain their expected acuity; when bright light is shone on the eye, light sensitive cells in the retina, including rod and cone photoreceptors and melanopsin ganglion cells, will send signals to the oculomotor nerve the parasympathetic part coming from the Edinger-Westphal nucleus, which terminates on the circular iris sphincter muscle. When this muscle contracts, it reduces the size of the pupil.
This is the pupillary light reflex, an important test of brainstem function. Furthermore, the pupil will dilate. If the drug pilocarpine is administered, the pupils will constrict and accommodation is increased due to the parasympathetic action on the circular muscle fibers, atropine will cause paralysis of accommodation and dilation of the pupil. Certain drugs cause constriction such as opioids. Other drugs, such as atropine, LSD, MDMA, psilocybin mushrooms and amphetamines may cause pupil dilation; the sphincter muscle has a parasympathetic innervation, the dilator has a sympathetic innervation. In pupillary constriction induced by pilocarpine, not only is the sphincter nerve supply activated but that of the dilator is inhibited; the reverse is true, so control of pupil size is controlled by differences in contraction intensity of each muscle. Another term for the constriction of the pupil is miosis. Substances that cause miosis are described as miotic. Dilation of the pupil is mydriasis. Dilation can be caused by mydriatic substances such as an eye drop solution containing tropicamide.
A condition called bene dilitatism occurs when the optic nerves are damaged. This condition is typified by chronically widened pupils due to the decreased ability of the optic nerves to respond to light. In normal lighting, people afflicted with this condition have dilated pupils, bright lighting can cause pain. At the other end of the spectrum, people with this condition have trouble seeing in darkness, it is necessary for these people to be careful when driving at night due to their inability to see objects in their full perspective. This condition is not otherwise dangerous; the size of the pupil can be a symptom of an underlying disease. Dilation of the pupil is known as mydriasis and contraction as miosis. Not all variations in size are indicative of disease however. In addition to dilation and contraction caused by light and darkness, it has been shown that solving simple multiplication problems affects the size of the pupil; the simple act of recollection can dilate the size of the pupil, however when the brain is required to process at a rate above its maximum capacity, the pupils contract.
There is evidence that pupil size is related to the extent of positive or negative emotional arousal experienced by a person. Not all animals
The sternal angle is the synarthrotic joint formed by the articulation of the manubrium and the body of the sternum. The sternal angle is a palpable clinical landmark in surface anatomy; the sternal angle, which varies around 162 degrees in males, marks the approximate level of the 2nd pair of costal cartilages, which attach to the second ribs, the level of the intervertebral disc between T4 and T5. In clinical applications, the sternal angle can be palpated at the T4 vertebral level; the sternal angle is used in the definition of the thoracic plane. This marks the level of a number of other anatomical structures: Position of the deep cardiac plexus Junction of the intra and extra pericardial parts of the superior vena cava. Line junction between C4 and T2 dermatome; the angle marks a number of other features: Carina of the trachea is deep to the sternal angle Passage of the thoracic duct from right to left behind esophagus Ligamentum arteriosum Loop of left recurrent laryngeal nerve around aortic archThe angle is in the form of a secondary cartilaginous joint.
This is. A clinically useful feature of the joint is; this is because the manubrium angles posteriorly on the body of the sternum, forming a raised feature referred to as the sternal angle. The sternal angle is called the angle of Louis, but the reason for that name was lost. Once thought to be after Antoine Louis or Wilhelm Friedrich von Ludwig, it is now believed to be after Pierre Charles Alexandre Louis. Thoracic plane List of medical mnemonics Anatomy photo:18:st-0212 at the SUNY Downstate Medical Center - "Thoracic Wall: Bones"
The axillary lines are the anterior axillary line, midaxillary line and the posterior axillary line. The anterior axillary line is a coronal line on the anterior torso marked by the anterior axillary fold. It's the imaginary line that runs down from the point midway between the middle of the clavicle and the lateral end of the clavicle; the V5 ECG lead is placed on the anterior axillary line, horizontally with V4. The midaxillary line is a coronal line on the torso between the anterior and posterior axillary lines, it is a landmark used in thoracentesis, the V6 electrode of the 10 electrode ECG. The posterior axillary line is a coronal line on the posterior torso marked by the posterior axillary fold. List of anatomical lines http://www.meddean.luc.edu/Lumen/MedEd/MEDICINE/PULMONAR/apd/lines.htm
An anatomical plane is a hypothetical plane used to transect the human body, in order to describe the location of structures or the direction of movements. In human and animal anatomy, three principal planes are used: The sagittal plane or median plane is a plane parallel to the sagittal suture, it divides the body into right. The coronal plane or frontal plane divides the body into ventral portions; the transverse plane or axial plane divides the body into caudal portions. There could be any number of sagittal planes; the term cardinal refers to the one plane that divides the body into equal segments, with one half of the body on either side of the cardinal plane. The term cardinal plane appears in some texts as the principal plane; the terms are interchangeable. The following terms are defined in reference to the anatomical model being in the upright orientation: A transverse plane is parallel to the ground. A coronal plane is perpendicular to the ground. A sagittal plane is perpendicular to the ground, separating left from right.
The midsagittal plane is the specific sagittal plane, in the middle of the body. The midsagittal or median plane is in the midline. Median can refer to the midsagittal plane of other structures, such as a digit; the axes and the sagittal plane are the same for bipeds and quadrupeds, but the orientation of the coronal and transverse planes switch. The axes on particular pieces of equipment may or may not correspond to axes of the body since the body and the equipment may be in different relative orientations; when describing anatomical motion, these planes describe the axis along which an action is performed. So by moving through the transverse plane, movement travels from head to toe. For example, if a person jumped directly up and down, their body would be moving through the transverse plane in the coronal and sagittal planes. A longitudinal plane is any plane perpendicular to the transverse plane; the coronal plane and the sagittal plane are examples of longitudinal planes. Sometimes the orientation of certain planes needs to be distinguished, for instance in medical imaging techniques such as sonography, CT scans, MRI scans, or PET scans.
One imagines a human in the anatomical position, an X-Y-Z coordinate system with the y-axis going from front to back, the x-axis going from left to right, the z-axis going from up to down. The z-axis is up and the right-hand rule applies. In humans, reference may take origin from superficial anatomy, made to anatomical landmarks that are on the skin or visible underneath; as with planes and points are imaginary. Examples include: The midaxillary line, a line running vertically down the surface of the body passing through the apex of the axilla. Parallel are the anterior axillary line, which passes through the anterior axillary skinfold, the posterior axillary line, which passes through the posterior axillary skinfold; the mid-clavicular line, a line running vertically down the surface of the body passing through the midpoint of the clavicle. In addition, reference may be made to structures at the rib cage. In medicine, abdominal organs may be described with reference to the trans-pyloric plane, a transverse plane passing through the pylorus.
In discussing the neuroanatomy of animals rodents used in neuroscience research, a simplistic convention has been to name the sections of the brain according to the homologous human sections. Hence, what is technically a transverse section with respect to the body length axis of a rat may be referred to in rat neuroanatomical coordinates as a coronal section, a coronal section with respect to the body in a rat brain is referred to as transverse; this preserves the comparison with the human brain, whose length axis in rough approximation is rotated with respect to the body axis by 90 degrees in the ventral direction. It implies that the planes of the brain are not the same as those of the body. However, the situation is more complex, since comparative embryology shows that the length axis of the neural tube has three internal bending points, namely two ventral bendings at the cervical and cephalic flexures, a dorsal flexure at the midst of the hindbrain, behind the cerebellum; the latter flexure appears in mammals and sauropsids, whereas the other two, principally the cephalic flexure, appear in all vertebrates.
This more realistic concept of the longitudinal structure of vertebrate brains implies that any section plane, except the sagittal plane, will intersect vari